(a) Field of the Invention
The present invention relates to a catalyst system for preparing styrene polymer and a method of preparing styrene polymer using the same, more particularly to a catalyst system for preparing styrene polymer capable of preventing coagulation of polymer to the reactor by preventing gelation, offering high conversion ratio, simplifying polymer production and enabling product size control, and a method of preparing styrene polymer using the same.
(b) Description of the Related Art
Canada Patent No. 2,026,552 discloses a method of preparing styrene polymer having syndiotactic stereostructure using metallocene catalyst.
In general, methods of preparing polymers having syndiotactic stereostructure from styrene monomers are classified into the slurry method using inert organic solvent and the bulk method directly polymerizing monomers.
In the slurry method, a liquid phase polymerization reactor equipped with the conventional stirrer is used because gelation, which occurs during polymerization of syndiotactic styrene polymer in the bulk method, can be prevented. That is, no specially designed equipment is required. Also, continuous production is possible because the product is obtained in liquid phase. However, since the inert organic solvent should be at least 80% of reactants, a process of solvent separation and purification is indispensable. Also, since the catalytic activity is greatly decreased, this method is limited to catalyst development, testing and other small-scale processes and not appropriate for large-scale production.
The bulk method, wherein monomers are directly polymerized, is used dominantly because it requires no additional solvent separation and purification process and offers good catalytic activity. However, this method renders the problem of polymer coagulation on the reactor wall due to gelation. Thus, specially designed reactors are used to polymerize syndiotactic styrene monomers, which increases production cost and aggravates productivity.
A variety of reactors are being developed to solve the gelation problem. For example, U.S. Pat. No. 5,254,647 discloses a wiped surface reactor for preparing syndiotactic styrene polymer. This reactor mixes monomers using two pairs of conventional screws to prevent coagulation at low conversion range, where particle growth begins rapidly. Then, the monomers are transferred to a powder bed type reactor to prepare syndiotactic styrene polymer with high conversion ratio. Resultantly, relatively uniform polymer can be obtained despite of low mixing efficiency of the powder bed type reactor. However, the screw reactor has limited capacity and operability, and because the polymerization is performed at low conversion ratio the powder bed type reactor is indispensable to obtain high conversion ratio, which increases production cost.
U.S. Pat. No. 6,242,542 discloses a method and an apparatus of preparing syndiotactic styrene polymer by connecting back-mixing reactors in series or in parallel. And, U.S. Pat. No. 5,484,862 discloses an improved liquid phase powder bed type reactor. According to this patent, syndiotactic styrene polymer can be prepared continuously because a horizontal agitator disperses polymer powders used as initiator in liquid phase monomers.
However, all the conventional techniques focus on preventing gelation or breaking coagulated particles and cannot fundamentally solve the coagulation and adhesion problems during polymerization.
Accordingly, researches on method of preparing styrene polymer capable of preventing polymer coagulation by fundamentally preventing the gelation problem and offering high conversion ratio by maintaining polymerization catalytic activity are highly required.